DESCRIPTION (prepared by applicant): Results of the Diabetes Control and Complications Trial indicate that most patients with type 1 diabetes (T1DM) should receive intensive treatment to lower the risk of microvascular and neuropathic complications. It has been shown that strict diabetes control can be achieved in youth with T1DM but at the expense of unacceptably high frequency of severe hypoglycemic events, especially in younger patients. Moreover, pilot studies using new continuous glucose sensoring systems in youth with T1DM indicate that many glucose swings from high to low values are asymptomatic and are not detected by self blood glucose monitoring (SBGM). Thus the investigators are submitting an application to be a center in the Type 1 Diabetes in Children Research Network to evaluate the utility of continuous glucose monitoring devices in improving diabetes control and preventing hypoglycemia in youth with T1DM. As a first step, the investigators are proposing to validate the accuracy of the MiniMed Continuous Glucose Monitoring System (CGMS) in children with and without T1DM against frequent blood glucose measurements in an inpatient Clinic and Research Center setting. Next, the CGMS will be used in a large, cross-sectional study to characterize and compare the frequency and severity of hypo and hyperglycemia by age (pre-school versus school age versus adolescents), type of insulin treatment (injections versus pump), and by HbA1c level (within target versus above target). Validation and cross-sectional studies will also provide the opportunity to test the effectiveness of current management guidelines regarding carbohydrate counting and the composition of bedtime snacks, as well as the impact of afternoon exercise on nocturnal hypoglycemia. The investigators are also proposing a randomized, prospective clinical trial to examine whether repeated use of the CGMS every six weeks for 24 weeks in conjunction with conventional SBGM is more effective than SBGM alone in improving diabetes control, lowering the risk for hypoglycemia, and reducing patient?s and parents? anxiety and fears of hypoglycemia. The introduction of new methods of continuous glucose sensoring promises to be the most important advance in therapy of T1DM in the past 20 years. The resources for clinical research and the expertise in the Network will also allow the investigators to assess the usefulness for children with T1DM of current and future glucose sensoring systems in a scientifically rigorous and timely manner.